Why is it unsafe if the live wire and the neutral wire are the wrong way round?

Answer 1

From a purely electrical perspective, most items will run just fine if the hot wire and neutral are reversed. I like to say the electrons don't care. But any protection built into a piece of equipment is wired into the hot wire and you subvert this protection if you reverse the wiring.

In a light fixture, the NEC requires the neutral wire (usually white) be connected to the screw shell of the socket. This prevents the screw shell from being energized and it is the most accessible part when changing bulbs. If properly wired, the hot part of a socket is the "button" in the very bottom of the socket.

There are some items that require proper wiring and the only way to ensure this is done is to do it right every time.

Another way to explain it is, using a vacuum cleaner as an example, if the wiring is correct, the hot wire goes to the switch and only when the switch is on is the vacuum cleaner energized. If the wiring is reversed, all the wiring in the vacuum cleaner is energized even when the switch is off.

Answer 2

Switching the live and neutral wires can lead to incorrect polarization, potentially causing electrical devices to malfunction or become unsafe. It can also create a risk of electric shock, as appliances may still be energized even when the switch is off. Additionally, it can interfere with the proper functioning of safety devices such as circuit breakers and grounding systems.